Testing Mods

I'm testing two props. I've done several flights where I've climbed to altitude, gone level at four different power settings, descended to another altitude, repeated the power settings etc. I've recorded all this on my GRT EFIS. I've taken this data and converted to TAS at those density altitudes.

My question, is comparing the data. I have data for specific density altitudes with each configuration. But the density altitudes are not the same because each day was different temps, baro press etc. To compare two data points, I think I have to take the TAS and density altitude and convert to EAS at SL. Then take the difference in EAS at SL, convert back to TAS at the density altitude to see the difference in TAS. Does this make sense?

I found the CAS/Mach/TAS/EAS converter at www.hochwarth.com that I have used to convert from TAS to EAS and then take the EAS difference and convert back to TAS at altitude.

Is this valid? Is there a better way, other than flying the second flight at the same DA as the first?

Thanks

Jim Butcher

I'm rather rusty at this, but what you are trying to achieve is exactly what flight test departments do the World over every day of the week. I think the way to do it is first to correct to EAS, then correct to standard day conditions (15*C, 1013mb (29.97in) at sea level), and use a standard lapse rate. Now you have data sets that can be compared.

Pete

h&jeuropa said:

I'm testing two props. I've done several flights where I've climbed to altitude, gone level at four different power settings, descended to another altitude, repeated the power settings etc. I've recorded all this on my GRT EFIS. I've taken this data and converted to TAS at those density altitudes.

My question, is comparing the data. I have data for specific density altitudes with each configuration. But the density altitudes are not the same because each day was different temps, baro press etc. To compare two data points, I think I have to take the TAS and density altitude and convert to EAS at SL. Then take the difference in EAS at SL, convert back to TAS at the density altitude to see the difference in TAS. Does this make sense?

I found the CAS/Mach/TAS/EAS converter at www.hochwarth.com that I have used to convert from TAS to EAS and then take the EAS difference and convert back to TAS at altitude.

Is this valid? Is there a better way, other than flying the second flight at the same DA as the first?

Click to expand...

It is possible to correct cruise speed vs power data to a standard weight, altitude and temperature. Send me the following data for each test point and I'll have a crack at it:

Prop model,
Power,
TAS (including whether mph or knots),
Pressure altitude (or barometric altitude and altimeter setting),
OAT (including whether deg F or deg C), and
Weight.

Send me a PM once you have the data together, and I'll reply with the email address to send it to.

Get a friend in a similar aircraft to fly beside you at the same airspeed. Note both power settings and mixture. Make your mods/ prop change and the fly with the chase plane again using exactly the same power settings. Any difference in airspeed will be obvious.
This method removes most environmental influences and takes very little time to do. Make sure that the aircraft loads and c of g are similar to prior flights.